The back pressure on a steam turbine is determined by the temperature of the coolant in the condenser coils over which the turbine exhaust steam passes, and excessive back pressure on a steam turbine makes the machine inoperable. Thus, the temperature of the coolant must be carefully controlled to limit the back pressure for continued production of power.
Excessive back pressures occur when climatic conditions constrain or impair the effectiveness of a cooling tower, producing higher temperatures of the coolant returned to the condenser. Moreover, when such conditions prevail there has been no realistic, economical alternative other than to shut down the steam turbine.
The inefficiencies and deleterious effects attributable to high back pressures are, of course, well known to persons of ordinary skill in the design and operation of steam power plants. Moreover, various means have been devised to lower back pressures by reducing the temperature of the condenser coolant. For example, U.S. Pat. No. 2,982,864 discloses a few forms of apparatus which utilize some of the waste heat of a boiler to enchance cooling of the condenser coolant.